Epileptic seizures are characterized by excessive or abnormally synchronous neuronal activity. Neurologists recognize a wide variety of seizures. Partial onset seizures begin in one part of the brain; general onset seizures arise throughout the entire brain simultaneously. When partial onset seizures progress to involve much of the brain, they are said to have “secondarily generalized.” Some seizures result in the loss of conscious awareness and are termed “complex” seizures. So-called “simple” seizures may involve other symptoms, but consciousness is unimpaired. Seizure symptoms may include sensory distortions, involuntary movements, or loss of muscle tone. The behavioral features of a seizure will often reflect a function of the cortex where the abnormal electrical activity is found.
Physicians have been able to treat epilepsy by resecting certain brain areas by surgery and by medication. Brain surgery is irreversible, and is ineffective or is associated with neural morbidity in a sizable percentage of cases. Medication is the most prevalent treatment for epilepsy. It is effective in over half of patients, but in the reminder of the patients, the medication is either ineffective in controlling seizures, or the patients suffer from debilitating side effects. A more promising method of treating patients having epileptic seizures is by electrical stimulation of the brain.
Since the early 1970's, electrical brain stimulators have been used to provide more or less constant stimulation, the stimulation largely being unrelated to detected electrical activity.
Electrical stimulation of the nervous system has been used to suppress seizures. A device is described in Cooper et al. for stimulation of the cerebellum. See, “The Effect of Chronic Stimulation of Cerebellar Cortex on Epilepsy and Man,” I. S. Cooper et al. in The Cerebellum, Epilepsy and Behavior, Cooper, Riklan and Snyder eds., Plenum Press, N.Y., 1974. Others have utilized devices that stimulate the centromedian nucleus of the thalamus. See, “Electrical Stimulation of the Centromedian Thalamic Nucleus in Control of Seizures: Long Term Studies,” F. Velasco et al, Epilepsia, 36 (1): 63-71, 1995. Chaos Theory has been used to apply stimulation to a seizure focus in vitro to abort the seizure. See S. Schiff et al, “Controlling Chaos in the Brain,” Nature, 370: 615-620, Aug. 25, 1994.
Non responsive electrical stimulation devices have been used for significant periods. The devices and procedures did not constitute a panacea, however. For instance, a seventeen-year follow-up study shown in Davis et al. (“Cerebellar Stimulation for Seizure Control 17 Year Study,” Proceedings of the Meeting of the American Society for Stereotactic and Functional Neurosurgery, Pittsburgh, Pa., Jun. 16-19, 1991 and in Stereotact. Funct. Neurosurg. 1992; 58: 200-208) showed that less than one-half of the patients became seizure free, even though 85% showed some benefit.
In contrast, responsive stimulation, specifically electrical stimulation that is applied to the brain, has not yet been used to treat patients in long-term studies. This is true even though there are algorithms suitable for detection of the onset of an epileptic seizure. For instance, Qu et al. provide an algorithm said to recognize patterns of electrical activity similar to those developed while recording an actual epileptic seizure. See, Qu et al., “A Seizure Warning System for Long-Term Epilepsy Monitoring,” Neurology 1995; 45: 2250-2254. Similarly, Osorio, et al. have suggested an algorithm applied to signals from intracranial electrodes with good results. See Osorio et al., “A Method For Accurate Automated Real-Time Seizure Detection,” Epilepsia 1995, 36(supp. 4).
None of the cited documents describes procedures in which a non-responsive electrical stimulation signal is applied to the brain in a first mode and, upon detection of impending or of extant epileptiform electrical activity, a second responsive mode of stimulation is applied to the brain either with or without cessation of non-responsive stimulation.